Method of making sheet material



Patented July 25, 1939 PATENT orrica METHOD OF MAKING SHEET MATERIAL Hermann Heckel, Chicago, 111., assignor to Marbon Corporation, a corporation of Delaware No Drawing.

4 Claims.

This invention relates to a method for producing sheet material and more particularly relatively thin, self-sustaining, transparent sheet or film material from a proteinogenous substance.

When making proteinogenous sheet materials from casein, gelatin, albumin, and the like, it is customary to start with a water soluble form of the protein selected and insolubilize the protein by means of formaldehyde, tannic acid or some other hardening agent. Even an insolubilized protein sheet, however, is relatively sensitive to changes in the humidity of the atmosphere to which the material is subjected and has relatively low water resistance.

I have now found that if the hardened proteinogenous sheet material is brought to substantially the iso-electric point of the protein selected, the resulting sheet or film material has greater resistance to water and is less sensitive to changes in atmospheric humidity conditions. of casein, to which this invention is particularly directed, a sheet or film of an insolubilized casein body is first formed and the pH value of the sheet or film then adjusted to approximately the iso-electric point of casein, which has been found to be 4.6. The sheet or film may then be plasticized, as by means of glycerine, dried and conditioned to' increase the flexibility of the sheet or film and adapt it for use for wrapping purposes.

It is therefore an object of this invention to provide a method for preparing relatively thin, transparent, sheet or film material from protein ogenous substances, whereby the resistance of the sheet or film material to water, its strength and paper like qualities are greatly improved.

It is a further important object of this invention to provide a thin, self-sustaining, transparent sheet of an insolubilized proteinogenous substance having improved resistance to water and to extreme conditions of relative humidity and therefore suited for use in the wrapping ofarticles where the transparency of the wrapper is partic ularly desirable.

Other and further important objects of this invention will become apparent from the following specification and appended claims.

Although this invention is applicable to the forming of sheet and film material from various proteinogenous substances, such as casein, gelatin, albumen, zein, and the like, it will be particularly described in connection with the formation of casein sheet and film material inasmuch as casein is best suited for the carrying out of this invention. The initial step of my process comprises the formation of a film or sheet of an in- In the case Application December 24, 1934, Serial No. 758,940

solubilized casein compound. For this purpose, any water soluble caseinate may be used, such as an alkali metal caseinate or the reaction product of casein and an alkyl amine or hydroxy alkyl amine, and the resulting water soluble caseinate 5 rendered insoluble, or hardened, by the addition of formaldehyde, tannic acid or other hardening agents. This step of the process is well known to those skilled in this particular art and is described in the application for patent of myself and others entitled Sheet material and method of preparing the same, Serial No. 668,808, filed May 1, 1933, and the application of myself and. others entitled Method and apparatus for making transparent sheet material, Serial No. 630,- 406, now Patent No. 2,014,937.

As illustrative of this first step, a caseinsolution comprising about 13 to 14% casein is mixed with a 10% solution of formaldehyde and water, in the proportion of about 1 part of the formaldehyde solution to 22 parts of the casein solution. A plasticizer, such as glycerine, need not be added at this point, since it would be largely removed by the subsequent steps and can therefore more feasibly be incorporated at a later stage.

A self-sustaining, transparent sheet material is made in accordance with the processes described in the above mentioned applications for patent. It is suitable, for instance, to cast the solution of casein and formaldehyde, immediately after mixing, onto a traveling web or belt provided with a surface from which the sheet can be readily stripped when dry. After stripping the sheet from the forming belt, the pH value of'the casein body of which the sheet is composed is adjusted to approximately the iso-electric point of casein, namely, 4.6. It is not essential that the casein body be brought to exactly this pH value, since I have found that substantial advantages can be obtained by adjusting the pH to a value between 40 the range of 4.0 to 5.0, and preferably between 4.3 and 4.9.

The adjustment of the pH value of the casein compound is accomplished by passing the hardened caseinate sheet or film through an aqueous bath having a pH value less than 5.0 and preferably about 4.6 or less. Instead of continuously passing the sheet or film of the insolubilized caseinate through such a bath, the sheet may be immersed in a bath of this character for a sufllcient length of time to bring the pH value of the sheet to that previously mentioned and the sheet then removed, plasticized and dried.

The composition of the aqueous bath may be prepared in various ways by the use of acids, such as hydrochloric, sulphuric, acetic, and the like, or by the use of acid reacting salts, such as sodium bisulphate, potassium aluminum. sulphate, acid phosphate, and the like, or by a'mixture of acids and salts. A preferred bath isone having a pH of about 4.6 and containing a bufi'ering agent, such as'an acid sulphate or acid phosphate, so as to maintain approximately that pH.

It is also possible to use successive aqueous baths, passing the sheet of insolubilized caseinate first through a bath of relatively strong acid and then through a tempering bath to adjust the pH of the sheet to approximately the iso-electric point of casein. This adjustment is effected by a proper control of the time of immersion of the sheet' within the bath, the period of immersion varying in proportion to the thickness of the film. Ordinarily, sheets or films of 1 to 3 one thousandths of an inch are employed and films of this degree of thinness require a very short immersion time.

After the sheet or film has passed through the aqueous acid bath and the pH of the sheet or film has been adjusted as indicated, it is pref erably washed to remove any free acid, and then passed directly into an aqueous plasticizing bath, such as an aqueous solution of from 40 to 60% of glycerine. Other plasticizing agents, such as the water soluble glycols of the parafiin series, ethylene glycol, and the like, may suitably be employed. In passing through the plasticizing bath,

' the sheet or film takes up a small percentage,

usually between 5 and 20%, of. the plasticizing agent. Any plasticizing solution that adheres to the surfaces of the film or sheet material and that is not absorbed thereby can be removed by means of roller doctors, scrapers, or the like.

After being piasticized, the sheet or film is dried in the usual manner, as by festooning, and then conditioned by being subjected to air having a relative humidity of from 40 to 60%. The drying and conditioning may, however, be carried out simultaneously by controlling the humidity within the driers.

The resulting sheet or film has better water resistance than casen films prepared in the manner heretofore practiced. Furthermore, the sheet or film of my invention has more body, that is, it feels more like paper. It has greater strength at high relative humidity and can withstand humidities as low as 20% relative humidity without becoming unduly brittle or frangible.

It will be understood that other ingredients may be incorporated into the sheet forming material prior to casting the film, such as various natural or synthetic gums and resins, with or without waxes, mineral oils, and the like, together with emulsifying agents, such as a mixture of alkali metal salts of organic sulphonic acids. Chlorinated diphenyls and gum dammar, or mixtures of the chlorinated diphenyls with gum dammar, parafiin wax and a refined white mineral oil, are particularly satisfactory for imparting desired properties to the finished sheet or film, such as body", resistance to water, and the like. A suitable emulsifying or dispersing agent is a product known to the trade as Soap H, which comprises certain purified and neutralized hydrocarbon sulphonic acids obtained as a byproduct in the manufacture of the so-called white" oils. In such manufacture, a lubricant fraction of the oil is treated with fuming sulfuric acid and some of the resulting sulfonic acids, which are soluble in the oil, are separated from other sulfonic acids that remain as a black sludge in the excess acid.

, The oil portion is neutralized with caustic soda and extracted with alcohol. The extracted material, consisting mostly of the sodium sulfonates of the hydrocarbons, after further'alcoholic purification to eliminate the oil and sodium sulfate, is known as Soap H and is both 011 and water soluble and mixes well with the gums and resins used. Its function in my composition is to act as an emulsifying agent. It may be replaced by other suitable emulsifying agents, if desired, such as the triethanolamine sulfonate of hydrocarbons of the Soap H" type, or by triethanolamine oleate. Sulfonated castor oil may also be used to give the solution better wetting action toward the surface on which the film is cast.

The final film or sheet material of my invention is characterized by its clear transparency, its homogeneity and its freedom from specks, opaque particles or other blemishes. For most purposes the sheet or film material is cast as a very thin pellicle of the same relative thinness as cellulose acetate, regenerated cellulose, or like products that are used for wrapping purposes.

I am aware that numerous details of the process may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. The method of making relatively thin transparent self-sustaining sheet material suitable for wrapping purposes, which comprises casting a solution of a soluble caseinate and a hardening agent into a self-sustaining sheet, setting the sheet but without substantially drying the sheet, passing the same through an acid bath to bring the sheet to about its iso-electric point and then through a bath of glycerine to plastic'ze said sheet and drying said sheet.

2. The method of making sheet or film material which comprises forming a sheet or film of a caseinate, subsequently adjusting the pH of the sheet or film to approximately the iso-electric point of casein, and incorporating a plasticizing agent with the film.

3. The method of making self-sustaining transparent sheet or film material, which comprises forming a sheet or film of a hardened caseinate, passing said sheet or film through an aqueous solution having an acidity greater than a pH=5.0

to bring the pH of said sheet or film between =4.0 and pH=5.0, and immersing said sheet in a bath of a plasticizing agent to plasticize said sheet.

4. The method of making self-sustaining transparent sheet or film material, which comprises forming a sheet or film of an alkali metal caseinate hardened by formaldehyde, passing said sheet or film through an aqueous solution of an acid at such a rate as to bring the pH of said sheet or film between pH=4.0 and pH=5.0, and passing said sheet through a bath of a plasticizing agent for casein to plasticize said sheet.

HERMAN N HECKEL, 

